Problem: What is the range of the function $$r(x) = \frac{1}{(1-x)^2}~?$$ Express your answer in interval notation.
Explanation: Every real number can be expressed in the form $1-x$ for some real $x$. Thus, as $x$ runs through the real numbers, $(1-x)^2$ runs through all nonnegative values, and its reciprocal (which is $r(x)$) runs through all positive values. The range of $r(x)$ is $\boxed{(0,\infty)}$.